|Boyd, Nathan -|
|Smith, Richard -|
|Foster, Phil -|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 19, 2010
Publication Date: January 31, 2011
Citation: Brennan, E.B., Boyd, N.S., Smith, R., Foster, P. 2011. Comparison of rye and legume-rye cover crop mixtures for vegetable production in California. Agronomy Journal. 103(2):449-463. Interpretive Summary: Cover crop mixes are important in California agriculture and are commonly used in rotations with organic vegetables. Five cover crop mixes containing various amounts of legumes (common vetch, purple vetch, woolypod vetch, fava bean and pea) and rye were compared with a pure rye cover crop at two certified organic sites (Hollister and Salinas,CA). Three of the mixes had 90% legume and 10% rye seed, while two of the mixes had 60% legume and 40% oat seed. Weed suppression tended to be lower in rye and 60% legume mixes than in 90% legume mixes. Total cover crop dry matter (DM) production increased through the season and was higher at the high fertility versus low fertility site. Mixes with 90% legumes produced more legume DM at both sites. The data indicate that 60 to 85% of the plants in the rye-legume mixes should be legumes to achieve adequate legume DM to justify the high cost of legume seed.
Technical Abstract: Rye (Secale cereale L.) is an important cover crop in high-value vegetable production in California but legume-rye mixes have received little research attention. A 2-yr winter study on organic farms in Salinas and Hollister, CA evaluated ground cover, above ground dry matter (DM) and C:N, and weed suppression of rye and five novel legume-rye mixtures. The mixes had 60 or 90% legumes by seed weight and included bell bean (Vicia faba L.) vetch (V. dasycarpa Ten., V. benghalensis L.) and pea (Pisum sativum L.). Seeding rates were 90 (rye) and 140 (mixes) kg ha-1, and densities were 148 to 404 plant m-2. Early season ground cover was in order of rye > 60% legume mixes > 90% legume mixes. Weed DM and seed at mid-season tended to be lower in rye and 60% legume mixes, however weed suppression in any cover crop was not adequate to recommend the cover crops at the seeding rates used. Total cover crop DM at mid-season was 1.9 to 6.5 Mg ha-1 and differed by cover crop. Mid-season rye DM increased with rye density and mid-season legume DM increased with vetch density. Mid-season legume DM was at least two times higher in 90 than 60% legume mixes. Total cover crop DM at season end was 4.7 to 14.6 Mg ha-1 but seldom differed between cover crops within site and yr. Most cover crops accumulated more than 150 kg N ha-1 but seldom differed by season end. When legume DM comprised 17% or more of total mix DM, the C:N of DM at season end was consistently lower in mixes than rye. Rye growing alone had a higher C:N than rye in 90% legume mixes in some cases. Legume-rye mixes with 60% legume seed may not be cost-effective considering their high seed costs and relatively low legume DM, but mixes with 90% legume seed may help reduce the C:N of cover crop residue and thus hasten decomposition before vegetable planting.